Aneurysms, dissections, penetrating ulcers, intramural hematomas and/or transections may occur in blood vessels, and most typically occur in the aorta and peripheral arteries. Depending on the region of the aorta involved, the aneurysm may extend into areas having vessel bifurcations or segments of the aorta from which smaller “branch” arteries extend. Various types of aortic aneurysms may be classified on the basis of the region of aneurysmal involvement. For example, thoracic aortic aneurysms include aneurysms present in the ascending thoracic aorta, the aortic arch, and branch arteries that emanate therefrom, such as subclavian arteries, and also include aneurysms present in the descending thoracic aorta and branch arteries that emanate therefrom, such as thoracic intercostal arteries and/or the suprarenal abdominal aorta and branch arteries that emanate therefrom, such as superior mesenteric, celiac and/or intercostal arteries. Lastly, abdominal aortic aneurysms include aneurysms present in the aorta below the diaphragm, e.g., pararenal aorta and the branch arteries that emanate therefrom, such as the renal arteries.
The thoracic aorta has numerous arterial branches. The arch of the aorta has three major branches extending therefrom, all of which usually arise from the convex upper surface of the arch and ascend through the superior thoracic aperture. The brachiocephalic artery originates anterior to the trachea. The brachiocephalic artery (BCA) divides into two branches, the right subclavian artery (which supplies blood to the right arm) and the right common carotid artery (which supplies blood to the right side of the head and neck). The left common carotid (LCC) artery arises from the arch of the aorta just to the left of the origin of the brachiocephalic artery. The left common carotid artery supplies blood to the left side of the head and neck. The third branch arising from the aortic arch, the left subclavian artery (LSA), originates behind and just to the left of the origin of the left common carotid artery and supplies blood to the left arm. However, a significant proportion of the population has only two great branch vessels coming off the aortic arch while others have four great branch vessels coming of the aortic arch. As will be explained in more detail herein, the distance(s) between the great branch vessels varies considerably amongst patients and the anatomical variation of the aortic arch complicates treatment thereof.
For patients with thoracic aneurysms of the aortic arch, surgery to replace the aorta may be performed where the aorta is replaced with a fabric substitute in an operation that uses a heart-lung machine. In such a case, the aneurysmal portion of the aorta is removed or opened, and a substitute lumen is sewn across the aneurysmal portion to span it. Such surgery is highly invasive, requires an extended recovery period and, therefore cannot be performed on individuals in fragile health or with other contraindicative factors.
Alternatively, the aneurysmal region of the aorta can be bypassed by use of an endoluminally delivered tubular exclusion device, e.g., by a stent-graft placed inside the vessel spanning the aneurysmal portion of the vessel, to seal off the aneurysmal portion from further exposure to blood flowing through the aorta. A stent-graft can be implanted without a chest incision, using specialized catheters that are introduced through arteries, usually through incisions in the groin region of the patient. The use of stent-grafts to internally bypass, within the aorta or flow lumen, the aneurysmal site, is also not without challenges. In particular, where a stent-graft is used at a thoracic location, care must be taken so that critical branch arteries are not covered or occluded by the stent-graft yet the stent-graft must seal against the aorta wall and provide a flow conduit for blood to flow past the aneurysmal site. Where the aneurysm is located immediately adjacent to the branch arteries, there is a need to deploy the stent-graft in a location which partially or fully extends across the location of the origin of the branch arteries from the aorta to ensure sealing of the stent-graft to the artery wall.
To accommodate side branches, main vessel stent-grafts having a fenestration or opening in a side wall thereof may be used. The main vessel stent-graft is positioned to align its fenestration with the ostium of the branch vessel. In use, a proximal end of the stent-graft, having one or more side openings, is prepositioned and securely anchored in place so that its fenestrations or openings are oriented when deployed to avoid blocking or restricting blood flow into the side branches. Fenestrations by themselves do not form a tight seal or include discrete conduit(s) through which blood can be channeled into the adjacent side branch artery. As a result, blood leakage is prone to occur into the space between the outer surface of the main aortic stent-graft and the surrounding aortic wall between the edge of the graft material surrounding the fenestrations and the adjacent vessel wall. Similar blood leakage can result from post-implantation migration or movement of the stent-graft causing misalignment between the fenestration(s) and the branch artery(ies), which may also result in impaired flow into the branch artery(ies).
In some cases, the main vessel stent-graft is supplemented by another stent-graft, often referred to as a branch stent-graft. The branch stent-graft is deployed through the fenestration into the branch vessel to provide a conduit for blood flow into the branch vessel. The branch stent-graft is preferably sealingly connected to the main stent-graft in situ to prevent undesired leakage between it and the main stent-graft. This connection between the branch stent-graft and main stent-graft may be difficult to create effectively in situ and is a site for potential leakage.
In some instances, branch stent-grafts are incorporated into or integrally formed with the main stent-graft as extensions thereof. Such integral branch stent-grafts extensions are folded or collapsed against the main stent-graft for delivery and require complicated procedures, requiring multiple sleeves and guide wires, to direct the branch stent-grafts extension into the branch vessel and subsequently expand. Further, in some instances, such branch stent-grafts extensions tend to return to their folded or collapsed configuration, and thus do not provide an unobstructed flow path to the branch vessel. Because the position or location of integral branch stent-grafts extensions is fixed on the stent-graft, there is no opportunity to ensure that each integral branch stent-grafts extension is optimally aligned with their intended target branch ostium. Offset alignment between the integral branch stent-grafts extension and target branch can make cannulation and branch stent-graft deployment difficult and put the patient at risk for occlusive stroke. Thus, integral branch stent-grafts extensions are not optimized to treat all patient anatomical variations which significantly limit patient applicability for these designs.
Another approach for treating variations in patient anatomy is utilization of a custom designed endovascular stent-graft. However, custom designed stent-grafts require a significant lead time, i.e., 6-8 weeks, and are costly to design and manufacture.
Thus, there remains a need in the art for improvements in stent-graft structures for directing flow from a main vessel, such as the aorta, into branch vessels emanating therefrom, such as branch vessels of the aortic arch.